This invention relates to dispersant-viscosity improvers for lubricating oils, and oil compositions and concentrates containing such dispersant-viscosity improvers.
The viscosity of lubricating oils, particularly the viscosity of mineral oil based lubricating oils, is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity decreases at an undesirable rate.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers or as viscosity modifiers.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of mechanical devices such as internal combustion engines, automatic transmissions, etc. in suspension rather than allowing them to deposit as sludge or other deposits on the surfaces of lubricated parts.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, xe2x80x9cLubricants and Related Productsxe2x80x9d, Verlag Chemie Gmbh (1984), pp 185-193; C. V. Smalheer and R. K. Smith xe2x80x9cLubricant Additivesxe2x80x9d, Lezius-Hiles Co. (1967); M. W. Ranney, xe2x80x9cLubricant Additivesxe2x80x9d, Noyes Data Corp. (1973), pp 92-145, M. W. Ranney, xe2x80x9cLubricant Additives, Recent Developmentsxe2x80x9d, Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, xe2x80x9cSynthetic Oils and Additives for Lubricantsxe2x80x9d, Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
Dispersant-viscosity improvers are generally prepared by functionalizing, i.e., adding polar groups to, a hydrocarbon polymer backbone.
Hayashi, et al, U.S. Pat. No. 4,670,173 relates to compositions suitable for use as dispersant-viscosity improvers made by reacting an acylating reaction product which is formed by reacting a hydrogenated block copolymer and an alpha-beta olefinically unsaturated reagent in the presence of free-radical initiators, then reacting the acylating product with a primary amine and optionally with a polyamine and a mono-functional acid.
Chung et al, U.S. Pat. No. 5,035,821 relates to viscosity index improver-dispersants comprised of the reaction products of an ethylene copolymer grafted with ethylenically unsaturated carboxylic acid moieties, a polyamine having two or more primary amino groups or polyol and a high functionality long chain hydrocarbyl substituted dicarboxylic acid or anhydride.
Van Zon et al, U.S. Pat. No. 5,049,294, relates to dispersant/VI improvers produced by reacting an a alpha-beta unsaturated carboxylic acid with a selectively hydrogenated star-shaped polymer then reacting the product so formed with a long chain alkane-substituted carboxylic acid and with a C1 to C18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups or with the preformed product thereof.
Bloch et al, U.S. Pat. No. 4,517,104, relates to oil soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties then with polyamines having two or more primary amine groups and a carboxylic acid component or the preformed reaction product thereof.
Gutierrez et al, U.S. Pat. No. 4,632,769, describes oil-soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties and reacted with polyamines having two or more primary amine groups and a C22 to C28 olefin carboxylic acid component.
Steckel, U.S. Pat. No. 5,160,648 describes dispersant materials prepared by reacting highly condensed polyamines with carboxylic reactants and phenolic reactants.
Stambaugh et al, U.S. Pat. No. 4,146,489 relates to graft copolymers wherein the backbone polymer is a rubbery, oil soluble ethylene-propylene copolymer or ethylene-propylene diene modified terpolymer and the graft monomer is a C-vinyl pyridine or N-vinylpyrrolidone. They are described as providing dispersant properties to hydrocarbon fuels and combined viscosity index improvement and dispersant properties to lubricating oils for internal combustion engines. The graft copolymers are prepared by intimate admixture of backbone polymer, graft monomer and free radical initiator at a temperature below initiation temperature, followed by a temperature increase to or above initiation temperature.
Jost et al, U.S. Pat. No. 4,338,418 discloses a method of making a lubricating-oil additive which improves the viscosity index and has a dispersing and detergent action, which method comprises graft copolymerizing, onto an oil-soluble base polymer, from 0.5 to 10 parts of a polymerizable lactam together with 0.1 to 3 parts of a polymerizable N-heterocyclic compound, said parts being by weight of said base polymer, and the lubricating oil additives so produced.
Each of these patents is hereby expressly incorporated herein by reference.
For additional disclosures concerning multi-purpose additives and particularly viscosity improvers and dispersants, the disclosures of the following United States patents are incorporated herein by reference:
As noted above, dispersant viscosity improvers have been prepared via free radical grafting of vinyl nitrogen monomers onto a wide variety of hydrocarbon polymer backbones. Some vinyl nitrogen monomers such as N-vinyl pyrrolidone and dimethylaminoalkyl methacrylamides are usually easily grafted under free radical conditions. Other vinyl nitrogen monomers such as N-vinyl imidazole tend to resist grafting under free radical conditions.
It has now been found that simultaneous grafting of certain specific and well-defined combinations of two or more different nitrogenous vinyl monomers leads to more efficient grafting, especially of monomers that are difficult to graft employing more conventional techniques. Moreover, the graft copolymers obtained thereby demonstrate surprisingly outstanding dispersancy and sludge suspension properties.
It is a primary object of this invention to provide novel multi-purpose lubricant additives.
A more specific object is to provide multi-purpose additives directed to improving lubricant viscosities and dispersancy properties.
A further object is to provide processes for preparing such multi-purpose additives.
Another object is to facilitate grafting, under free radical conditions. of vinylic nitrogen containing monomers onto a hydrocarbon backbone.
Still another object is to provide lubricants having improved dispersancy and viscosity properties.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.
The present invention is directed to a graft copolymer useful as a dispersant-viscosity improver for lubricating oil compositions. The graft copolymer comprises a hydrocarbon polymer having graft polymerized thereon at least two nitrogen containing units, at least one of the nitrogen containing units being derived from at least one of a neutral N-(lower hydrocarbyl group)- (meth)acrylamide and a neutral N,N-di-(lower hydrocarbyl group)- (meth)acrylamide, wherein the total number of carbon atoms in the lower hydrocarbyl groups does not exceed 9, and at least one of the nitrogen containing units being derived from at least one vinylic nitrogen containing heterocyclic compound.
This invention is also directed to a process for preparing the graft copolymer, methods for improving the efficiency of free radical grafting of vinylic nitrogen containing heterocyclic monomers onto hydrocarbon polymers, additive concentrates and lubricating oil compositions comprising the copolymers of the invention, and methods for improving the viscometrics and dispersancy characteristics of lubricating oil compositions.